We colonised a pyrethroid-resistant population of An. sinensis in the laboratory, which provides a fundamental model for genetic studies of this important malaria vector.

Background Current methods to classify local and imported malaria infections depends primarily on patients travel history, which can have limited accuracy. Genotyping has been investigated as a complementary approach to track the spread of malaria and identify the origin of imported infections.Methods An extended panel of 26 microsatellites (16 new microsatellites) for Plasmodium falciparum was evaluated in 602 imported infections from 26 sub-Saharan African countries to the Jiangsu province of People's Republic of China. The potential of the 26 microsatellite markers to assign imported parasites to their geographic origin was assessed using a Bayesian method with MCMC (Markov Chain Monte Carlo) as implemented in the program Smoothed and Continuous Assignments (SCAT) with a modification to incorporate haploid genotype data.Results The newly designed microsatellites were polymorphic and are not in linkage disequilibrium with the existing microsatellites, supporting previous findings of high rate of recombination in sub-Saharan Africa. Consistent with epidemiology inferred from patients travel history, we found no evidence for local transmission; nearly all genetically related infections were identified in people who traveled to the same country near the same time. The smoothing assignment method assigned imported cases to their likely geographic origin with an accuracy (Angola: 59%; Nigeria: 51%; Equatorial Guinea: 40%) higher than would be achieved at random, reaching statistical significance for Angola and Equatorial Guinea.Conclusions Routine genotyping is valuable for malaria case classification and program evaluation in an elimination setting. Method for assigning geographic origin of mammals based on genetic data were adapted for malaria and showed potential for identification of the origin of imported infections.

A field population of Culex pipiens pallens was collected from Nanjing, China on July in 2000 and reared in an insectarium. Larvae were subjected to single, mixed, and alternating exposure to deltamethrin and/or fenthion, and the surviving early 4th instars were reared for establishment of adult colonies. Larvae from the colonies were then subjected to the same selection pressures over the subsequent 15 generations. Resistance rates and ratios were measured as LC50 values derived from larval bioassays. In populations exposed to deltamethrin or fenthion alone (single exposure), resistance levels rose rapidly. The LC50 values for deltamethrin and fenthion alone were 29.3 and 1.565 mg/liter, respectively, and the ratios of resistance were 697.6- and 24.8-fold, respectively. Exposure to a mixture of deltamethrin and fenthion (1:1; mixed selection) reduced the development of resistance. The LC50 value and ratio of resistance for the mixture of deltamethrin and fenthion were 0.607 mg/liter and 14.8-fold, respectively, at generation 15. Exposure to alternating treatments of deltamethrin and fenthion (alternating selection) showed an even lower development of resistance. For the alternating treatments, the LC50 value and ratio of resistance to deltamethrin were 0.795 mg/liter and 17.7-fold, respectively (generation 14), and those to fenthion were 0.219 mg/liter and 3.6-fold, respectively (generation 15). Together, these results indicate that the single continuous insecticide selection generated a much more severe resistance than a mixture and/or alternating treatments.

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